It will switch on but I can't use it. It shows a photo of a folder.

@frances71608 sounds like your camera is stuck trying to read a directory structure that is missing, corrupted, or locked. From what you are describing your camera goes directly into Playback Mode and cannot communicate properly with the SD card while it should go into live view shooting mode.

Check your cameras mode selector to make sure it isn't set to playback mode. If that is working okay, you do need to check your SD-Card. Remove the card and make sure it is not write protected. Depending on the SD card you are using, there should be a will be a little tab that you can slide to unprotect.

If it is not write protected then it is possible that you have a failed card and, worst case scenario, is that your card reader has failed. Try a new SD card or format the card that you are currently using. Remember that you will lose any information stored on that card.

Also, check the pins on the card reader to make sure there are no bend or broken pins and that the pins are not obstructed by any debris etc. A few puffs of "canned" air can help to clean those.

LEt us know what you find out.